[PATCH] ARM: fdt: copy TF-A reserved memory into fdt passed to Linux

[Alexander Sverdlin]

Hi Paul,

On Sun, 2026-06-14 at 23:06 +0200, Paul Kocialkowski wrote:
> > > But another thing we do overwrite current is the cpu idle states, which
> > > are added by fdt_add_cpu_idle_states in tf-a. These are only set when the
> > > SCP firmware is available (which is checked at run-time) and they are
> > > never propagated to the final device-tree. Including the definitions
> > > statically would result in cpu idle calls done even without the SCP
> > > firmware, which would probably fail (although maybe some states can
> > > still be supported).
> > 
> > Do you refer to some unmerged code? Didn't find it in the current TF-A
> > sources...
> 
> fdt_add_cpu_idle_states is in common/fdt_fixup.c and it is called by the
> common allwinner code in plat/allwinner/common/sunxi_prepare_dtb.c based
> on the sunxi_psci_is_scpi check (which currently always returns false
> for A133).

sorry, I misunderstood you initially, I though there are some data structures
of the SCP firmware which are being overwritten by Linux, but it turns out,
you refer to idle-states node and compatible = "arm,idle-state" subnodes...
But contrary to /reserved-memory nodes for TF-A, these are fixed for a SoC
model, even if you'd like to load SCP firmware at a different address, right?

It looks to me that all other machines/SoCs do define this stuff statically
in the Linux DT.

I have a feeling, that idle-states node is more like a "contract" or an API
between FW and Linux and is supposed to change less frequently, while loading
TF-A to a completely different address would be transparent to Linux, as long
as we properly copy /reserved-memory nodes.

-- 
Alexander Sverdlin.